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计算:1/3*6+1/6*9+1/9*12+.1/3n(3n+3)
题目详情
计算:1/3*6+1/6*9+1/9*12+.1/3n(3n+3)
▼优质解答
答案和解析
1/3*6+1/6*9+1/9*12+.1/3n(3n+3)
=1/3*[3/3*6+3/6*9+3/9*12+.3/3n(3n+3)]
=1/3*[1/3-1/6+1/6-1/9+1/9-1/12+.+1/3n-1/(3n+3)]
=1/3*[1/3-1/(3n+3)]
=1/3*[(3n+3-3)/3(3n+3)]
=1/3*[3n/3(3n+3)]
=n/3(3n+3)
=1/3*[3/3*6+3/6*9+3/9*12+.3/3n(3n+3)]
=1/3*[1/3-1/6+1/6-1/9+1/9-1/12+.+1/3n-1/(3n+3)]
=1/3*[1/3-1/(3n+3)]
=1/3*[(3n+3-3)/3(3n+3)]
=1/3*[3n/3(3n+3)]
=n/3(3n+3)
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